1. Field of the Invention
The present invention relates to a process for producing a film member formed of a heat-resistant resin having a metallic thin film accumulated thereon, and also relates to a process for producing an endless belt formed with the film member.
2. Description of the Related Art
A film member formed by accumulating a thin film of an electroconductive metal, such as copper and aluminum, on a thin plate formed by impregnating a thin plate or a core material of a heat-resistant resin with a heat-resistant resin has been widely used as a substrate for a printed circuit. In an image forming apparatus using a dry toner, such as those of an electrophotographic system and an electrostatic recording system, an endless film formed by accumulating a heat-resistant resin and a metallic thin film has been often used as an intermediate transfer member for temporarily carrying a toner image.
The toner image formed by attaching a toner to an electrostatic image is transferred to the intermediate transfer member, and the toner image is heated by electromagnetic induction to be simultaneously transferred and fixed to a recording medium.
Such an image forming apparatus will be roughly described below.
FIG. 7A is a schematic constitutional view of the image forming apparatus, which is a full color laser printer of an electrophotographic system. FIG. 7B is an enlarged view of an important part of the image forming apparatus.
The image forming apparatus has a photosensitive drum 1, on the surface of which a latent image is caused by differences in electrostatic potential, and also has, around the photosensitive drum 1, an exposing part having a charging unit 2 for substantially uniformly charging the surface of the photosensitive drum 1, a laser scanner 3 and a mirror 4 for forming a latent image by irradiating the photosensitive drum 1 with laser light corresponding to respective color signals; a rotational developing unit 5 having toners of four colors, cyan, magenta, yellow and black, for visualizing the latent image on the photosensitive drum with respective color toners; an intermediate transfer member 6 in the form of an endless belt supported to be capable of circulating in one direction; a cleaning unit 7 for cleaning the surface of the photosensitive drum after transferring; and an exposing lamp 8 for static elimination the surface of the photosensitive drum 1.
The intermediate transfer member is hung between a driving roller 10 and a tension imparting member 11, and a pressure roller 12 is provided to face the driving roller 10 to sandwich the intermediate transfer member 6. An electromagnetic induction heating unit 13 for heating the intermediate transfer member 6 is provided on the upstream of the circulating direction of the intermediate transfer member 6 with respect to the position, at which the driving roller 10 faces the pressure roller 12.
The apparatus further has a paper supplying roller 16 and a resist roller 17 for transmitting a recording material contained in a paper supplying unit 15 one by one, and also has a recording material guide 18 for supplying the recording material between the intermediate transfer member 6 and the pressure roller 12.
The electromagnetic induction heating unit 13 has an excitation coil 13 as shown in FIG. 8, and forms an alternating magnetic field penetrating the intermediate transfer member 6. The intermediate transfer member 6 has a substrate layer 6a having accumulated thereon an electroconductive layer (electromagnetic induction heating layer) 6b and a releasing layer 6c having good releasing property, and an eddy current B is formed in the electroconductive layer 6b by the alternating magnetic field. The electroconductive layer 6b is heated by the eddy current to heat and fuse the toner image carried on the surface.
In the image forming apparatus, the toner images of respective colors formed on the photosensitive drum 1 are transferred to overlap one by one on the intermediate transfer member 6 by a bias voltage applied between the photosensitive drum 1 and the driving roller 10, so as to form a full color toner image. The toner image is fused by electromagnetic induction heating of the electroconductive layer 6b of the intermediate transfer member, and accumulated to the recording material to fix thereto by pressure between the pressure roller 12 and the driving roller 10. As a result, the toner image is simultaneously transferred and fixed to the recording material.
The intermediate transfer member 6 is, for example, an endless belt formed by accumulating a copper thin film having a thickness of about from 1 to 50 xcexcm to a film member formed of a heat-resistant resin, such as thermosetting polyimide, aromatic polyamide (aramid) and a liquid crystal polymer, having a thickness of from 50 to 200 xcexcm. The liquid crystal polymer exhibits liquid crystalline property in a dissolved state or a molten state, and a thermotropic liquid crystal polymer exhibiting liquid crystalline property in a molten state has excellent properties, such as a high strength, a high heat resistance, a low linear expansion coefficient, a high insulating property, a low hygroscopicity and a high gas barrier property. Therefore, the application thereof is expanding not only to the field using the liquid crystalline property, but also as a mechanical member and fibers.
As described in the foregoing, it has been known that the production of a film member formed by accumulating a metallic thin film and a layer of a heat-resistant resin is conducted by a method, in which a film of a heat-resistant resin and a metallic foil are attached to each other with an adhesive, and a method, in which a metallic thin film is formed on a film of a heat-resistant resin by electroplating, electroless plating or vapor deposition.
However, in the method of attaching with an adhesive, the reliability in adhesive force is poor when the metallic thin film is repeatedly subjected to electromagnetic induction heating.
In the method of forming a metallic thin film on a heat-resistant resin, it is generally difficult to firmly attach a metallic thin film, such as copper, to a heat-resistant resin, such as polyimide and aromatic polyamide (aramid). Therefore, techniques for improving the adhesiveness have been proposed, and for example, JP-A-5-299820 proposes a technique, in which a metallic vapor deposition film is formed on polyimide, and then an electron beam heating vapor deposition copper layer and an electroplating copper layer are consecutively accumulated thereto.
JP-A-6-316768 discloses a technique, in which fluorine is contained in polyimide, and in order to make the fluorine function as adhesive sites, the first step etching treatment is conducted by using an aqueous solution containing hydrazine, and the second step etching treatment is conducted with naphthalene-l-sodium, so as to make copper be liable to attach thereto. JP-A-7-216225 discloses a technique, in which the adhesiveness of a plating metallic film by previously mixing metallic powder in a polyimide precursor is improved.
As for the case where the heat-resistant resin is aromatic polyamide (aramid), JP-A-6-256960 proposes a technique, in which the resin is subjected to an etching treatment with an aqueous solution containing hydrazine and an alkali metal hydroxide, and then a catalyst imparting treatment for electroless plating is conducted.
However, in the conventional techniques, in which a metallic thin film is formed after molding the heat-resistant resin, sufficient adhesiveness cannot be obtained, and the production process cannot be simplified.
In the case a liquid crystal polymer is used as the heat-resistant resin, on the other hand, a film form resin can be directly heat-fused with a metallic foil, but in general, the film member of the liquid crystal polymer is strongly oriented on molding and is liable to split off in one direction.
The invention has been made in view of the foregoing circumstances and is to provide a process for producing, in simple procedures, a heat-resistant resin film having a metallic thin film accumulated thereto and an endless belt of a heat-resistant resin having a metallic thin film accumulated thereto that are excellent in mechanical characteristics.
According to an aspect of the invention, the process for producing a heat-resistant resin film having a metallic thin film contains the steps of: coating a substrate with a releasing agent; forming a metallic thin film thereon; forming a layer containing a heat-resistant resin thereon; and peeling an accumulated body containing the heat-resistant resin and the metallic thin film from the substrate.
According to another aspect of the invention, the process for producing an endless belt having a metallic thin film contains the steps of: forming a metallic thin film on an inner surface of a cylindrical substrate; forming a layer containing a heat-resistant resin thereon; and peeling an accumulated body containing the heat-resistant resin and the metallic thin film from the substrate.
It is preferred in the invention that the step of forming the layer of a heat-resistant resin contains the steps of: placing a polyamide acid solution in an interior of the cylindrical substrate; rotating the cylindrical substrate in a circumferential direction to make the solution be a layer on the metallic thin film; and subjecting the solution to imidization by heating to form a film member containing polyimide.
The invention also provides, as another aspect, an endless belt having a metallic thin film produced by such a process that contains the steps of: forming a metallic thin film on an inner surface of a cylindrical substrate; forming a layer containing a heat-resistant resin thereon; and peeling an accumulated body containing the heat-resistant resin and the metallic thin film from the substrate.
The invention also provides, as another aspect, an endless cylindrical belt having a metallic thin film containing a layer containing a heat-resistant resin on an inner surface of the metallic thin film, the metallic thin film being a metallic foil, the metallic thin film having a junction of joining both ends of the metallic thin film, and the layer of a heat-resistant resin having no junction.
The invention also provides, as another aspect, an apparatus for forming an image containing: an image carrier, in which a latent image caused by differences in electrostatic potential is formed on an endless surface thereof; a developing unit visualizing the latent image by attaching toner powder containing a thermoplastic resin to the image carrier; an intermediate transfer member, on which a toner image formed on the image carrier is temporarily transferred; and a transferring and fixing unit heating the toner image on the intermediate transfer member and press-fixing the molten toner image on a recording medium, wherein the intermediate transfer member is an endless belt described above, and the transferring and fixing unit contains an electromagnetic induction coil arranged to face the intermediate transfer member.